This invention relates to a surgical prosthetic joint designed to replace a metatarsal-phalangeal articulation of a human toe, and methods of its installation.
Various types of prosthetic joints have been developed to replace diseased or damaged human toes. Toe joint prosthesis are known in the art and commonly comprise two components having opposed ball and socket parts. A metatarsal component of the prosthetic joint is designed to be surgically implanted on the end of a resected metatarsal bone of the joint being replaced. A phalangeal component of the prosthetic joint is designed to be surgically implanted at a resected end of a phalanx bone of the joint being replaced. The metatarsal component is commonly constructed from a metal alloy and provides a convex bearing surface to replace and function as the original convex surface of the metatarsal bone of the toe joint. The phalangeal component has a concave surface that slides over the convex surface of the metatarsal component and is designed to replace and function as the original socket surface of the phalanx bone of the toe joint. In the prior art, the metatarsal component and the phalangeal component have been secured to the resected ends of the metatarsal and phalangeal bones such as with pegs or pins that extend from the components opposite their respective ball and socket surfaces. In the art, the pegs or pins fit with the bones to hold the prosthetic joint components in their proper positions relative to the metatarsal and phalangeal bones.
In preparation for the implantation of conventional prosthetic joints, the end of the metatarsal bone of the joint to be replaced is resected to dimensions that provide a close fit between the metatarsal component of the prosthetic joint and the resected end of the metatarsal bone. The phalanx bone of the joint being replaced is also resected to dimensions that provide a close fit between the phalangeal component of the prosthetic joint and the resected end of the phalanx bone. A groove or hole can be cut into each of the resected ends of the bones, to receive the above discussed peg or pin protrusions of the metatarsal and phalangeal components. The metatarsal and phalangeal components of the prosthetic joint are implanted in their proper positions on the resected ends of the respective metatarsal and phalanx bones. This is done by inserting the protrusions of the components into the cuts made in the ends of the respective bones and cementing the components in place.
When a metatarsal bone of a joint is diseased or injured to the extent that it requires replacement with a prosthetic joint, often the top dorsal surface and the bottom plantar surface of the metatarsal bone are also diseased or injured. These surfaces must be replaced to provide for a full range of articulating movement of the phalanx bone relative to the metatarsal bone. However, some prior art prosthesis provide a metatarsal component with a convex bearing surface that does not extend far enough up over the top of the resected metatarsal, or far enough down under the bottom of the resected metatarsal, to replace the diseased or injured dorsal and plantar surfaces of the metatarsal bone.
Also, many of the known prosthetic joints designed to replace the metatarsal-phalangeal articulation of the human toe have a metatarsal component with a bone confronting surface angled from the horizontal that confronts and is cemented to a resected bottom surface of the metatarsal bone. These prior art metatarsal components provide either very little or no horizontal surface area of contact between the metatarsal component of the prosthesis and the resected metatarsal bone to distribute the force exerted on the metatarsal component from walking over an area of the metatarsal bone. Also, the angled surfaces of some prior art prosthesis metatarsal components resolve the force exerted on the metatarsal component from walking into vertical and horizontal components of force. This results in the horizontal component of force tending to separate the metatarsal component of the prosthesis from the metatarsal bone, and requires that the metatarsal component of the prosthesis be cemented in place, or that some other measures be taken to ensure that the component does not separate from the bone. In addition, many of the pegs or pins provided on the metatarsal and phalangeal components of the prior art prosthetic joints do not adequately resist torsion forces exerted on the components. These prosthesis components can become loose with time and can cause problems with one surface of one of the prosthetic components sliding over a surface of the other prosthetic component that is not properly oriented relative to the one component.
The present invention overcomes the shortcomings of existing prosthesis. The present invention provides a prosthetic joint that replaces the metatarsal-phalangeal articulation of a human toe and resists torsion forces applied to the prosthetic joint. The present invention further has a horizontal bone confronting surface that distributes the forces exerted on the metatarsal component over a greater area of the metatarsal bone. Moreover, the present invention provides a metatarsal component with an extended bearing surface adapted to extend above and below the resected end of a metatarsal bone to reproduce the extent of articulation of the phalanx bone relative to the metatarsal bone in a healthy toe joint.
It is therefore an object of the present invention to provide an improved human toe prosthetic joint for metatarsal-phalangeal articulation that resists torsion. It is an object for such a toe prosthetic joint to reduce the effect of force applied to the metatarsal through walking by distributing the force over a greater area of the metatarsal. Moreover, it is an object for such a toe prosthetic joint to provide an extended range of articulation of the phalanx bone relative to the metatarsal bone.